1. Field of the Invention
The present invention relates to an improved tubular pipe and, more specifically, to a tool joint stress relief groove.
2. Description of the Background
Tubular goods such as drill pipe normally comprise pin and box tool joints welded to opposite sides of a pipe body. An upset region of increased wall thickness is typically provided on each side of the drill pipe body to allow a strong weld between the drill pipe body and the two tool joints. Due to the differences in these parts of the drill pipe as discussed hereinafter, stresses created by drilling tend to be non-uniform over the length of the drill pipe.
When drilling through a deviated or arcuate wellbore, the drill string formed by many individual drill pipes normally conforms to the arcuate contour of the well bore by bending accordingly. The stresses induced in each drill pipe by such bending are typically well below the yield strength of the pipe. However, when the drill pipes are rotated for rotary drilling while held in a bent position by the arcuate well bore, the stress becomes cyclical and fatigue failure may occur. Such a failure may cause the drill string to part. If the drill string parts, drilling must stop for a considerable time until the lost portion of pipe is fished out of the well bore and the integrity of the remaining drill pipe is checked. The more arcuate the well bore, the greater will be the cyclical stress on the drill pipe. Furthermore, fishing operations may become difficult in a highly deviated hole. Thus, there is an increased risk of losing the well and also the remainder of the expensive drill string in such highly deviated wells i.e. those wells in which fatigue failure is most likely to occur.
Due to discontinuities in wall thickness of the pipe, the stress created in a drill pipe due to bending in conformance with the well bore is not normally uniform along the entire length of the drill pipe. If failure occurs, the pipe is most likely to fail at the place in the drill pipe which experiences the most cyclically applied stress. In many cases, that place is the juncture of the normally substantially regular drill pipe body and the upset region. In this region, the wall thickness of the pipe is increased to form the upset portion by either a change in outside diameter, inside diameter, or both. The increased wall thickness permits a strong weld between the pipe body and the tool joint. The upset portion of tin e pipe with thicker walls is less likely to bend to match the shape of the arcuate well bore. Thus, the portion of the pipe with relatively thinner walls, especially that portion near the upset, may bend more than other parts of the drill pipe in order for the drill pipe to conform to the well bore. Since this portion of the pipe may experience significantly greater stress than other portions of the pipe, the stress created thereby may be near or above the pipe's endurance limit as discussed hereinafter even though it is below the yield strength of the pipe. Thus, rotation of the drill pipe may cause premature failure at this portion of the pipe.
Because of the significant time loss and cost involved whenever the drill string parts, a long felt need exists in the industry for a solution to failure caused in drill pipes due to cyclically applied stresses. Those skilled in the art will appreciate the present invention which substantially alleviates this problem.